Aircraft, such as airliners, usually include one or more batteries for supplying electrical energy to components of the aircraft. For example, an airliner may comprise one or more Lithium-ion or lead acid batteries for supplying electrical energy to an auxiliary power unit (APU) to start the auxiliary power unit. The batteries may be recharged during operation of the aircraft by a generator coupled to an auxiliary gearbox of a gas turbine engine
In some instances, the power density of such batteries may not be sufficiently high to power some components of the aircraft. For example, a Lithium ion or lead acid battery may not have a sufficiently high power density to power critical loads of an aircraft during flight, such as, pumps, controls, or to restart a gas turbine engine in the event of a system failure. In order to provide sufficient electrical power, the aircraft may comprise a plurality of such batteries electrically connected in series to one another. However, this may increase the weight of the aircraft and thereby reduce the fuel efficiency of the aircraft.